Fungi Flashcards
What species of candida accounts for 50% of all candida infections?
c. albicans
How does oral candida infection occur?
usually the result of the outgrowth of an endogenous pop of candida organisms no longer held in check by innate body defenses
What are the three main body defenses that usually help prevent candida from infecting the oral cavity?
saliva and normal bacterial flora and t cell mediated immunity
For what kinds of patients is candida especially dangerous (ie. what cell deficiencies)?
t-lymphocyte defects or neutropenic pts with disseminated infection have very poor prognosis
What is a fungal infection that is considered an AIDS-defining illness? What are associated problems?
candida esophagitis
dysphagia/difficulty swallowing. often consume soft carb-rich diets as a result- bad cycle, since such diets lower the environmental pH, which makes candida happy
What are the morphologic forms of candida?
yeast, hypha, pseudohypha
What is candida vulvovaginitis? what species cause this infection? How is it treated
“yeast infection”
candida albicans
candida glabrata (higher rates of treatment failure)
fluconazole
What distinguishes C. albicans from other candida species?
ability to form germ tubes- nascent hypha from yeast forms
What form(s) of candida is/are most adhesive?
germ tube and mature hyphae
How does candida adhere to the oral cavity?
host transglutaminase interacts with candida integrin or proline-rich molecules to provide a stable, covalent attachment.
How does C. albicans invade tissue?
growing hyphal tip actively penetrates tissue. facilitated by secretion of hydrolytic enzymes
What are the three main layers of the candida cell wall?
mannoprotein layer
glucan layer
chitin layer
What is the purpose of the mannan/mannoprotein layer in candida?
attachement and permeability barrier
What is the role of the glucan layer in candida?
structural integrity of the cell
What is the role of the chitin layer in candida?
structural role, esp. at the site of new cell formation
What are polyene antibiotics? What are the two relevant drugs? How does it work?
example: amphotericin B and nystatin
this binds to ergosterol in the plasma membrane and increases its permeability.
What are special considerations with the use of amphotericin B>
amphotericin B cannot be orally administered because its not water soluble.
Are polyene antibiotics -cidal or -static drugs? Any special considerations/concerns?
cidal
yes! very low therapeutic window
What are the azole derivatives (imidazoles and triazoles)? (examples) How do they work?
miconazole and fluconazole
perturb membrane stucture and function by inhibition of a cytochrome P450 analog which participates in the synthesis of membrane components
What is miconazole? What class and how administered?
azole derivative (fungal P450 inhibitor and membrane synthesis disruptor) topical application
What is fluconazole? What class and how administered?
triazole derivative
P450 analog inhibitor- membrane synthesis disruptor
systemic admin
Are azole derivatives -cidal or -static agents?
static
Echinocandins. How do they work? Example?
caspofungin
target beta-glucans by inhibiting glucan synthesis
Are echinocandins -cidal or -static agents?
cidal
Flucytosine: how does it work? How administered? special considerations?
nucleic acid analog that inhibits DNA synthesis. good oral absorption
relatively low toxicity but must be used in conjunction with other drugs because resistance develops easily
What is cryptococcus neoformans? Who is susceptible? Morphology? reservoir?
most rapidly emerging fungal pathogen for AIDS pts
yeast form only
pigeon droppings and eucalyptus leaves
What is the main virulence factor associated with cryptococcus neoformans? What is the main therapeutic challenge?
- polysacchride capsule
- reistant to echinocandins
Aspergillus: who is susceptible? Where is it acquired? What happens during infection
- those with severe breakdown in cell-mediated defenses
- acquired by inhalation of ubiquitous spores
- grow as filamentous form at the site of infection to form a fungal ball or aspergilloma
- secrete hydrolytic proteases
How do you treat aspergillus infection?
amphotericin B
What is dermatophytosis? What layer of the skin is infected? What are the two main genera?
fungal infection of keratinized tissue
stratum corneum is infected
trichophyton and microsporum
What is an effective drug against the dermatophytes?
allylamines, like terbinafine/lamisil
How do allylamines work?
inhibit squalene epoxidase, which is needed for ergosterol formation. leads to membrane disruption and cell death.
What are two licensed allylamines?
lamisil/terbinafine and naftifine
How is terbinafine administered? How is naftifine administered?
terbinafine is available both orally and topically
naftifine is only topical
What are the 5 traits common to systemic mycoses caused by environmentally acquired fungi?
- dimorphism- grow in yeast form at 37C (as mycelium at 25C)
- route of infection- inhalation of spores
- disseminated infection, esp. in immunocompromised
- geographic predilection
- immunologic response, usually granulomatous inflammation
What are some symptoms of systemic mycoses?
often asymptomatic
may present with severe pulmonary disease and weight loss
you must differentiate btw systemic mycoses and TB
Where is histoplasma capsulatum common? Where is it found in the environment?
ohio, mississippi and missouri river valleys
found in bird and bat feces
acute and chronic pulmonary infections
Pathology of histoplasma capsulatum
reporduces inside macrophages
usually asymptomatic
some people get headaces, fevers, chills, cough, chest pain.
Coccidioides immitis: where is it common geographically?
dsserts of northern mexico and SW US.
Coccidioides immitis- typical presentations? severe presentations
often asymptomatic
sometimes flu symptoms- fever, dry cough, eosinophili, etc.
some get bone infection and meningitis (less than 1%)
Blastomyces dermatitidis. where is it found geographically and environmentally?
soil of states east of the mississippi
What are symptoms of bastomyces dermatitidis?
rarely asymptomatic
usually pleuritic chest pain, fever, chills, productive cough
severe cases involve weight loss, night sweats, skin ulcers, potential death. TREAT AGGRESSIVELY.
Paracoccidioides brasiliensis: morphology. where is it from?
pilots wheel- multiple buds off a single parent cell
endemic to brazil and latin america
What is the epi of paracoccidioides brasiliensis? What are the most common sites of infection?
- WAY more men than women (female hormones prevent infection?)
- mouth and nose
What are the four systemic mycoses?
coccidioides immitis, histoplasma capsulatum, blastomyces dermatitidis, and para coccidioides brasiliensis
